Something of interest occurred last night in my kitchen. It started when I
was preparing to pitch (add yeast to) my batch of beer.

I needed to boil and purify some water, so I filled a 10 oz. clean coffee
cup 1/3 full with spring water. I heated the water in my microwave oven at
full power for 3 minutes. I was busy sanitizing my equipment and hadn't
noticed if the water had actually boiled. So, after a few minutes, I set
the microwave for another 2 minutes at full power to be sure. I returned to
my sanitation duties.

49 seconds later, I heard a small, muffled, explosion. I turned to see that
the door of the microwave had blown open and water was dripping from all
interior surfaces of the microwave. The coffee cup was intact. My wife,
who was 2 rooms away, heard the explosion. She wanted to know "What the
hell happened?"

Can anyone tell ME? How/why did the water explode? Superheated steam?

The cup was clean and not covered. The water was western Pennsylvania (USA)
spring water. The microwave is 9 years old. (I don't know the power
rating.)

Regards,

John Gerthoffer
Software Engineer
American Auto-Matrix, Inc.
Smart Building Solutions

>49 seconds later, I heard a small, muffled, explosion. I turned to see that
>the door of the microwave had blown open and water was dripping from all
>interior surfaces of the microwave. The coffee cup was intact. My wife,
>who was 2 rooms away, heard the explosion. She wanted to know "What the
>hell happened?"

HUAHUAHUAHUAHUA, ROTF!!! ;oD

This is one of the funniest, and most dangerous thing that can happen with a microwave.

Why water boils? It boils because the water vaporizes, and gets lighter as temperature increases. Water normally does not heat equally, so the water vapour goes from the hottest part to the coldest part, making bubbles we are used to see. But imagine: In a microwave, everything gets heated equally, so, where is the coldest part of the water? Simply, it doesn't have the coldest part. It could be the walls of the cup, but since it's heated equally by the hot water, the temperature gradient is not enough to make bubbles.

This is the only way (beyond pressurization) water can go above 100ºC.

Funny is that water vaporizes and gets absorved by the water, like gaseous water. it has, of course, a limit. But see: If you have water at 110ºC, superheated, and ANYTHING that's colder than it touches the water, or a small blow of the wind cools a part of water/can, the entire system EXPLODES in a stream of boiling water. It's marvelous to see!!! Nothing good to happen with you, though.

It's important to remember: Try to never heat water on the microwave. If you have to do it, put a spoon made of wood, or plastic inside of it. But please, DON'T DO IT. It's dangerous. It's hazardous. It can happen to everyone. Imagine if before the explosion, you had to take that can of water in your hands. It would explode in your face as soon as it was taken out the microwave oven. And the results woudn't be aestethically pleasant, at least. :o)

You should consider yourself lucky that the door's interlock shut the
klystron tube circuit off! Else you'd be cooking! Any microwave oven that
the door comes open like that is pretty dangerous to keep anround! Yes, I've
had the same thing happen to me (without the door opening, however). As the
water boiled off, the pressure of the microwave's cavity changed causing the
water to "superheat".

the actual problem is not so much the heating of the water,
but the nucleation of the bubbles. you know how they
sometimes 'seed' clouds to make it rain, because there is
moisture but nothing to condense on? what you have here is
similar: the water is hot enough to boil, but has nothing ot
nucleate on if youve filtered it and it hasnt even got a
lonely little air bubble or speck of dust. any disturbance
then will cause a cascade of nucleations and the whole thing
blows.

So the solution of putting in something to nucleate on is a
good one. this is one place where judicious sloppiness will
come out ahead of aniseptic sterile technique. i would
suggest locating (and scrubbing off) a 'magic pebble' of some
worthy local stone, reserved for the sacred duty of
preventing overboils. use of the 'magic pebble' will ensure
good beer etc.
alice

> >49 seconds later, I heard a small, muffled, explosion. I turned to see that
> >the door of the microwave had blown open and water was dripping from all
> >interior surfaces of the microwave. The coffee cup was intact. My wife,
> >who was 2 rooms away, heard the explosion. She wanted to know "What the
> >hell happened?"
>
> HUAHUAHUAHUAHUA, ROTF!!! ;oD
>
> This is one of the funniest, and most dangerous thing that can happen with a microwave.
>
> Why water boils? It boils because the water vaporizes, and gets lighter as temperature increases. Water normally does not heat equally, so the water vapour goes from the hottest part to the coldest part, making bubbles we are used to see. But imagine: In a microwave, everything gets

heated equally, so, where is the coldest part of the water? Simply, it doesn't have the coldest part. It could be the walls of the cup, but since it's heated equally by the hot water, the temperature gradient is not enough to make bubbles.
>
> This is the only way (beyond pressurization) water can go above 100ºC.
>
> Funny is that water vaporizes and gets absorved by the water, like gaseous water. it has, of course, a limit. But see: If you have water at 110ºC, superheated, and ANYTHING that's colder than it touches the water, or a small blow of the wind cools a part of water/can, the entire system
EXPLODES in a stream of boiling water. It's marvelous to see!!! Nothing good to happen with you, though.
>
> It's important to remember: Try to never heat water on the microwave. If you have to do it, put a spoon made of wood, or plastic inside of it. But please, DON'T DO IT. It's dangerous. It's hazardous. It can happen to everyone. Imagine if before the explosion, you had to take that can of
water in your hands. It would explode in your face as soon as it was taken out the microwave oven. And the results woudn't be aestethically pleasant, at least. :o){Quote hidden}

>klystron tube circuit off! Else you'd be cooking! Any microwave oven that
>the door comes open like that is pretty dangerous to keep anround! Yes, I've

Funny to remember someday I was fixing a Radar unit, and (I was a beginner in this field) i felt some heat on my pulse...AAAAAAGGGHHH!!! My (all metal) watch got the microwaves and begun to heat!!! It hurted, I have some markings on the pulse till today...

>Hi all,
>
>Something of interest occurred last night in my kitchen. It started when I
>was preparing to pitch (add yeast to) my batch of beer.
>
>I needed to boil and purify some water, so I filled a 10 oz. clean coffee
>cup 1/3 full with spring water. I heated the water in my microwave oven at
>full power for 3 minutes. I was busy sanitizing my equipment and hadn't
>noticed if the water had actually boiled. So, after a few minutes, I set
>the microwave for another 2 minutes at full power to be sure. I returned to
>my sanitation duties.
>
>49 seconds later, I heard a small, muffled, explosion. I turned to see that
>the door of the microwave had blown open and water was dripping from all
>interior surfaces of the microwave. The coffee cup was intact. My wife,
>who was 2 rooms away, heard the explosion. She wanted to know "What the
>hell happened?"
>
>Can anyone tell ME? How/why did the water explode? Superheated steam?
>
>The cup was clean and not covered. The water was western Pennsylvania (USA)
>spring water. The microwave is 9 years old. (I don't know the power
>rating.)

A similar phenomenon has been reported with reheated coffee which
foams up when removed. There seem to be at least 2 possible factors,
and a combination of these may be involved. 1) The water at the bottom has slightly exceeded 100 deg.C, but the
weight of the water above exerts pressure, which increases the boiling
point slightly. Uneven microwave distribution could cause water at the
bottom to be hotter than that at the top, for a while at least. As
soon as a bubble forms, the turbulence disrupts this unstable
equilibrium and the superheated water vaporises rapidly due to the
pressure drop, blowing the water above out of the container.
2) If the water is very still, and has boiled before, there may be no
dissolved air and/or nucleation sites in the container to help
initiate nucleation of bubbles, so again the water becomes heated
slightly above its boiling point, and vaporises rapidly as soon as the
first bubble forms.

/2) If the water is very still, and has boiled before, there may be no
/dissolved air and/or nucleation sites in the container to help
/initiate nucleation of bubbles, so again the water becomes heated
/slightly above its boiling point, and vaporises rapidly as soon as the
/first bubble forms.

AFAIK nucleation is the key here.
On the initial heating all air bubbles etc have been driven out.

On next heating ALL the fluid is brought o 100 C uniformly.
Recall that Water can exist as liquid AND vapour at 100C. As you add energy
to the water it does not increase in temperature until it has gauned enough
energy to fully vaporise. If you heta a body of water completely "smoothly"
you can convert ALL of it to just below the steam point but it will still be
liquid. Now introduce the slighest gradient and away it goes. Some molecules
will "eelcty" to diminish there higher energy states and the adjacent ones
pick up the energy. ALL the container is still at 100 C but some water moves
closer to the steam point. Of there are any points of higher temperature
(side of cup etc) then the change to pure steam is available and the
remaining water is carried out with the steam.

I've heard about this but never seen it.
Must try it :-) !!!
(Yeah, I know).

I've experienced this before when i used to make coffee using my
microwave.
Heat cup of water in microwave for 2 1/2 minutes
Remove cup from microwave (no bubbles therefore no completly boiled,
RIGHT)
Put in one teaspoon of instant coffee
Spend twenty minutes cleaning up kitchen because instant coffee has gone
everywhere.

It's good to know there is a scientific reason for this, I just thought
my cup was possessed
Regards
Stuart

>
> /2) If the water is very still, and has boiled before, there may be no
> /dissolved air and/or nucleation sites in the container to help
> /initiate nucleation of bubbles, so again the water becomes heated
> /slightly above its boiling point, and vaporises rapidly as soon as the
> /first bubble forms.
>
> AFAIK nucleation is the key here.
> On the initial heating all air bubbles etc have been driven out.
>
> On next heating ALL the fluid is brought o 100 C uniformly.
> Recall that Water can exist as liquid AND vapour at 100C. As you add energy
> to the water it does not increase in temperature until it has gauned enough
> energy to fully vaporise. If you heta a body of water completely "smoothly"
> you can convert ALL of it to just below the steam point but it will still be
> liquid. Now introduce the slighest gradient and away it goes. Some molecules
> will "eelcty" to diminish there higher energy states and the adjacent ones
> pick up the energy. ALL the container is still at 100 C but some water moves
> closer to the steam point. Of there are any points of higher temperature
> (side of cup etc) then the change to pure steam is available and the
> remaining water is carried out with the steam.
>
> I've heard about this but never seen it.
> Must try it :-) !!!
> (Yeah, I know).
>
> --
> http://www.piclist.com hint: To leave the PICList
> TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu

> >49 seconds later, I heard a small, muffled, explosion. I turned to see that
> >the door of the microwave had blown open and water was dripping from all
> >interior surfaces of the microwave. The coffee cup was intact. My wife,
> >who was 2 rooms away, heard the explosion. She wanted to know "What the
> >hell happened?"
>
> HUAHUAHUAHUAHUA, ROTF!!! ;oD
>
> This is one of the funniest, and most dangerous thing that can happen with a microwave.
>
> Why water boils? It boils because the water vaporizes, and gets lighter as temperature increases. Water normally does not heat equally, so the water vapour goes from the hottest part to the coldest part, making bubbles we are used to see. But imagine: In a microwave, everything gets heated equally, so, where is the coldest part of the water? Simply, it doesn't have the coldest part. It could be the walls of the cup, but since it's heated equally by the hot water, the temperature gradient is not enough to make bubbles.
>
> This is the only way (beyond pressurization) water can go above 100ºC.
>
> Funny is that water vaporizes and gets absorved by the water, like gaseous water. it has, of course, a limit. But see: If you have water at 110ºC, superheated, and ANYTHING that's colder than it touches the water, or a small blow of the wind cools a part of water/can, the entire system EXPLODES in a stream of boiling water. It's marvelous to see!!! Nothing good to happen with you, though.
>
> It's important to remember: Try to never heat water on the microwave. If you have to do it, put a spoon made of wood, or plastic inside of it. But please, DON'T DO IT. It's dangerous. It's hazardous. It can happen to everyone. Imagine if before the explosion, you had to take that can of water in your hands. It would explode in your face as soon as it was taken out the microwave oven. And the results woudn't be aestethically pleasant, at least. :o)
>
> As people on tv say: kids, don't try it at home!
>
> --------------8<-------Corte aqui-------8<--------------
>
> All the best!!!
> Alexandre Souza
> xandinhoEraseME.....interlink.com.br
> Linux User #85093
>
> --------------8<-------Corte aqui-------8<--------------
>
> --
> http://www.piclist.com hint: To leave the PICList
> EraseMEpiclist-unsubscribe-requestmitvma.mit.edu

I don't get it. I have microwaved water before and have never seen these
results. There are a couple of exceptions though:

BTW: I was making Mac and cheese...

I usually nuke about 4 cups of water in a 2 quart bowl (uncovered), not a
coffee cup.
I add just a pinch of salt. Does lowering the boiling point affect the
experiment?
I set the power on HIGH (700 Watt microwave) for 10 minutes. Maybe the
wattage isn't high enough?

Throwing the macaroni in doesn't seem to make it explode at all. Have I
just been lucky all these years?

> I don't get it. I have microwaved water before and have never seen these
> results. There are a couple of exceptions though:
>
> BTW: I was making Mac and cheese...
>
> I usually nuke about 4 cups of water in a 2 quart bowl (uncovered), not a
> coffee cup.
> I add just a pinch of salt. Does lowering the boiling point affect the
> experiment?

yes. salt lowers the boiling point. so does sugar. this
morning i did a deliberate boilover using our filtered water.
the water actually had begun to nucleate and form bubbles, i
added a spoon of sugar very slowly and got it to foam up.
because the sugar has to work its way down through the
chaotically foaming water, you can actually see the downward
progression of the water flashing to steam. I learned long
ago (via burnt fingers) to start with just a pinch of sugar,
not to dump it in.

> I set the power on HIGH (700 Watt microwave) for 10 minutes. Maybe the
> wattage isn't high enough?
>
even a 500 watt will work. use water that is 'still', that
is, that isnt still fizzy from the aeration in the tap. also,
a really clean, smooth glass bowl.

> Throwing the macaroni in doesn't seem to make it explode at all. Have I
> just been lucky all these years?
>
my microwave cookbooks recommend using a container about 4
times in volume of what's cooking, to contain these
boilovers/overboils. this problem is not a new one, but
everyone still seems to discover it for themselves.

It seems to depend a lot on the dish, and I wouldn't be surprised if the
air circulation in the microwave affects it as well.

I used to have instant oatmael quite frequantly:
fill a bowl with water
nuke the water for a few minutes (it does come to a boil)
Take the bowl out very carefully and slowly
(if I took it out too fast it would boil quickly for a second)
Dump the contents of the packet in
Watch it boil again for a few seconds on my counter

It rarely happened with any other bowl that I had, though I didn't do a
study of which bowls worked and why.

This is probably why all of the microwaveable instant foods I see now have
you add the product, then microwave, whereas the stove directions are to
boil the water, then add the product.

>
> I don't get it. I have microwaved water before and have never seen these
> results. There are a couple of exceptions though:
>
> BTW: I was making Mac and cheese...
>
> I usually nuke about 4 cups of water in a 2 quart bowl (uncovered), not a
> coffee cup.
> I add just a pinch of salt. Does lowering the boiling point affect the
> experiment?
> I set the power on HIGH (700 Watt microwave) for 10 minutes. Maybe the
> wattage isn't high enough?
>
> Throwing the macaroni in doesn't seem to make it explode at all. Have I
> just been lucky all these years?
>
> On Mon, 27 Nov 2000, P.J. McCauley wrote:
>
> > Be careful doing this! Checkout the link below, there is an anecdote there
> > about it.
> > www.ecs.noaa.gov/NMFS/safetyNewsletter.html
> >
> > Joe
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
> > piclist-unsubscribe-requestSTOPspamspam_OUTmitvma.mit.edu>
> >
> >
> >
>
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> http://www.piclist.com hint: To leave the PICList
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Yow! i stand corrected(reference: CRC handbook). hes right,
dissolved stuff raises the BP. so the boilover then is
principally caused by nucleation on the added ingredients,
and actually the boiling point is rising during the
explosion. So the boilover phenom is carried by the
nucleation. hmm. now im thinking that the blow-open-the-
oven eruptions are caused when the mechanical vibration of
the fan causes nucleation at the bottom of the container,
which propagates upwards constrained by the sides of the
vessel. this could certainly be a bigger mess than the
adding-sugar style of eruption that goes from the top down.

> > yes. salt lowers the boiling point. so does sugar. this
>
> Hmm. I seem to remember two sets of three words each that talk about such
> stuff:
>
> 1) Freezing point depression
> 2) Boiling point elevation
>
> That is, salt water would seem to boil at a higher temperature than pure
> water. Is there something special about water?
>
> Who out there is a chem. geek?
>